A level shifter is an electronic device that converts digital signals from one logic level to another logic level. In digital circuits, a logic level is one of a finite number of states that a digital signal can have. Logic levels are usually represented by the voltage difference between the signal and ground. A digital-to-analog converter (DAC) is a system that converts a digital signal into an analog signal. The level shifter is a critical component for high speed DAC operations.
Conventional level shifters have a DC static current which results in large power consumption. Due to hot carrier injection, the conventional level shifters suffer from reliability problems because overshot current causes premature degradation of the integrated circuit. As a result, the life time of the circuit is reduced. Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term “hot” refers to the effective temperature used to model carrier density. Since the charge carriers can become trapped in the gate dielectric of a MOS transistor, the switching characteristics of the transistor can be permanently changed. Hot-carrier injection is one of the mechanisms that adversely affects the reliability of semiconductors of solid-state devices.
Advanced DAC designs require operations to be performed at high speeds (e.g., higher than 18 GHz), which cannot be achieved by conventional level shifter designs. In addition to high speed performance, advanced DAC designs require low power and reliable level shifters.